American Urological Association - (Deep) Leiomyoma
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(Deep) Leiomyoma

Image A

Image B

  • LM of deep soft tissues is uncommon and is most often found in the retroperitoneum.
  • Patients are in 40s-60s; more common in women.
  • Manifest as slow growing painless mass.
  • Gross:
    • Well-circumscribed gray-white tumor with no necrosis.
    • Range 5-20 cm, retroperitoneal LM may grow big.
  • Histology:
    • Intersecting fascicles of deeply acidophilic spindle cells.
    • Nuclei have blunt ends ("cigar-shaped") (image A) & (image B).
    • No significant cellular pleomorphism.
    • Retroperitoneal LM may have mitosis (but not >5/HPF).
  • Immunohistochemistry: actin+, desmin+.
  • True LMs are benign lesions that merely require excision with a small cuff of normal tissue.
  • DDX: Other spindle cell tumors that are low-grade appearing.
    • Schwannoma: wavy nuclei, hypo and hypercellular areas, Verocay bodies and S100+, actin-
    • GIST: related to bowel wall, perinuclear vacoulations; CD117+, DOG1+.